Added cycle detection to Variant

We accidentally enabled nested tables previously, and now it errors properly when the tables contain cycles. Before you'd get (or at least I got) a nice lua stack overflow error.

--HG--
branch : minor

src/common/Variant.h

@@ -27,6 +27,7 @@
 
 #include <cstring>
 #include <vector>
+#include <set>
 
 namespace love
 {
@@ -63,7 +64,7 @@ public:
 
 	Type getType() const { return type; }
 
-	static Variant fromLua(lua_State *L, int n, bool allowTables = true);
+	static Variant fromLua(lua_State *L, int n, std::set<const void*> *tableSet = nullptr);
 	void toLua(lua_State *L) const;
 
 private: